Service Experience with Sandwich Construction—Some Approaches to Problems in Aircraft Applications

The developments after World War II in the fields of structural metal-bonding adhesives and lightweight core materials gave the aircraft and missile designer a new structural form—sandwich construction. Through structural and environmental laboratory testing, he has learned much about this material and has gained confidence in its ability to perform satisfactorily. However, performance of the sandwich in service is the real key to its usefulness and limitations and provides the final data needed for objective evaluation. This paper presents some of the service history and experience which The Martin Co. has encountered in applying adhesive-bonded sandwich structure to aircraft and missiles over the past 15 years. It is hoped that the knowledge gained from these experiences will result in improved designs, intelligent utilization, and increased confidence in the structural sandwich. To a limited degree, the performance of structural adhesives under environmental conditions can be determined through laboratory tests. Military specifications [1, 2] describe tests and establish requirements for salt spray exposure, humidity exposure, and immersion in various aircraft fluids, which the materials are required to meet before they are accepted for military use. However, these tests are primarily screening tests and do little for the prediction of service life and performance.